Write up of current status of 100-Mo irradiations¶

I irradiated three targets of 100-Mo at three different energies. One of which was above the 7.79MeV threshold energy for the 100Mo(p,2n)99mTc reaction. The other two were below this threshold energy.

Below you find the interactive plot of the cross section analysis of the 100-Mo irradiations. If you hover over the data points you should see more information about the particular data point, such as the author of the measurement, the beam energy and the exact cross section value. (If you press shift + left click anywhere on the plot you can pan around the plot)

The irradiation above the threshold energy was done mainly to help me get started with my analysis code and such that I can compare the results with existing literature (EXFOR Data). As one can see our measurement at ~8.4MeV agrees quite well with the literature data, so I assume that the analysis code is working correctly. I also compared a few values with measurements from Gaia and our calculations agree within uncertainty.

In [23]:
# open the plotly plot and re-render it here
with open("../../cs-100Mo.html", "r", encoding="utf-8") as f:
    html_content = f.read()
HTML(html_content)
Out[23]:

My concerns about the energy spread¶

Since we use attenuators to reduce the beam energy, the beam energy is not sharp. I had concerns that the peak we see (below the energy threshold) might just be due to the fact that some protons are above the 7.79MeV threshold energy and thus produce 99mTc via the 100Mo(p,2n)99mTc reaction. However, I ran a SRIM simulation with 10'000 particles and Al attenuator of 1488um (which results in around ~6.38MeV, the same as in our las measurement), the histogram of the energy distribution is shown below.

As one can see, no protons are above the 7.79MeV threshold energy, so I assume that if there are any protons above the threshold energy, they are very few and thus the contribution to the 140.5 keV peak is negligible.

image

Other gamma lines¶

After our last meeting on thursday Ihor asked me to look for different peaks in the gamma spectra. The spectra shown below is a screenshot from InterSpect from the last irradiation (target 4, t4) done at ~6.38MeV recorded over a 10 hour period. In InterSpect I was able to add all Tc(m) isotopes to indicate the gamma lines of the different isotopes (thats why its a screenshot, at the end of the file you can find the spectra again as a interactive plot where you can zoom in to see the lines)

The only peaks that had a significant intensity and I was able to match were the following:

  • 140.5 keV (99mTc)
  • 307.03 keV (101Tc)
  • 545.47 keV (101Tc)

So my assumption is that we only produced 99mTc and 101Tc in significant amounts.

alt text

The hope is now that the 140.5 keV peak is only from the 100Mo(p,²n)99mTc reaction.

I think 101Tc could be from the 100Mo(p,gamma)101Tc reaction, since I found (on IAEA) that the cross section for this reaction is within the same order of magnitude as the cross section we calculated for the 99mTc in this measurement. See screenshot below

image

Where does the 140.5 keV peak come from?¶

Now we need to try to exclude or quantify all other contributions to the 140.5 keV peak, i.e. the decay of 99Mo to 99mTc.

I considered the following two reactions that could produce 99Mo:

  • 100Mo(p,np)99Mo
  • 98Mo(p,gamma)99Mo

Below you find the corresponding cross section data from IAEA for these reactions. alt text

As one can see only the 98Mo(p,gamma)99Mo reaction has a significant cross section at the energies we plan to irradiate at. But since we do not see any 99Mo peaks in the gamma spectra I still think that we did not produce any 99Mo in significant amounts. Especially since the amount of 98Mo in our target is very low (0.18%).

Next Steps¶

But to make sure that the 140.5 keV peak is indeed only from the 100Mo(p,²n)99mTc reaction I will try to do repeated spectra measurements of the next sample (new spectra every 6 hours) and see if the peak intensity changes exponentially or according to the Batemann equation over time.

If we see a exponential decay of the peak intensity, we can assume that the 140.5 keV peak is indeed only from the 100Mo(p,²n)99mTc reaction and not from any other reaction. If we see a decay according to the Batemann equation we must assume that we produced 99Mo either via 100Mo(p,np)99Mo or 98Mo(p,gamma)99Mo.

The next sample will be irradiated at ~6.06MeV, slightly lower than the last one.

My Questions¶

  • Are my assumptions regarding the production of 99Mo correct? Are there other reactions I sould consider?
  • In general do you agree with my next steps? Or how could we try to disentangle the contributions to the 140.5 keV peak? Maybe with Gaias approach of using a different enrichments and then the linear system of equations to disentangle the contributions.

Appendix¶

Below is the spectra of the last irradiation (target 4, t4) as shown in the InterSpect screenshot as an interactive plot. You can zoom in to see the peaks more clearly.

In [24]:
# open the plotly plot and re-render it here
with open("./enrMo100-t4-8.txt.html", "r", encoding="utf-8") as f:
    html_content = f.read()
HTML(html_content)
Out[24]:
In [ ]: